1. Field of the Invention
The present invention relates to the field of explosion-proof electric motors, more specifically to an explosion-proof braking device for an explosion-proof electric motor.
2. Background Art
In the prior art, an explosion-proof self-braking electric motor is equipped with a brake in its rear part which is integral with the structure of the motor as one piece, so as to ensure the desired explosion-proof characteristics.
The known type of explosion-proof self-braking electric motor has a shaft which is integral with an electromagnetic brake disk: when current is supplied to the electromagnet, the brake disk opens and the electric motor is released from the brake; on the contrary, when the electromagnet receives no current, the brake disk is locked by the braking device, thus generating a braking torque that locks the motor shaft.
Said explosion-proof characteristics are subject to certification and must comply with strict regulations. Consequently, the explosion-proof self-braking electric motor is difficult and costly to manufacture, also because both the motor and the brake, since they are built as one piece, need to be changed depending on the nominal electric and mechanical characteristics required by the specific application.
The brake part of said motor requires more frequent checks and maintenance than the motor part. When installed in plants located in hazardous areas, it is not possible to carry out maintenance work on just one part of a device having a single flame-proof or explosion-proof enclosure, since said enclosure, being a single piece, cannot be opened on site. Therefore, the whole motor needs to be removed and brought to an authorized service shop: this may require stopping the plant because the entire device has to be replaced.
The need to ensure the explosion-proof characteristic makes the brake much more difficult to manufacture. It must be fitted with an enclosure where the connections of its mating parts must have mechanical characteristics subject to binding and strict tolerances, which are verified by certification bodies (e.g., French INERIS) through tests carried out under pressure in order to ascertain the correct behaviour of the device in the event of an explosion. For example, if a spark is generated inside in the presence of inflammable gases (such as acetylene) propagating both outside and inside the product, e.g., in a petrochemical plant, then an explosion may occur: in such a case, the spark must not be allowed to come out and the product must not explode.
WO2005/098258 describes an modular-disk electromagnetic brake that can be mounted to the front flange of an electric motor. However, the technical features of such a device can be improved in order to ensure the explosion-proof characteristic independently of the electric motor to which it will be coupled.